Despite our best efforts to treat pain, epidemiological studies report that only 50% of cancer patients obtain 70% or greater pain relief with current analgesic medications . Such clinical insufficiency is presumably the result of treatment which is directed at only parts of a widespread (and largely unidentified) neural network which comprises pain processing. Over the past several decades, anatomical mapping and distribution of neurons in the central nervous system (CNS) responding to noxious thermal, mechanical and chemical stimuli have been extensively investigated by electrophysiological techniques. Although these techniques provided considerable information, a major drawback is the limited number of neurons from which recordings can be simultaneously made. For example, it is extremely difficult to monitor the simultaneous activity of large populations of neurons that are distributed over the neuraxis. Functional magnetic resonance imaging (fMRI) is now used to measure metabolic activity in the brain. In this preliminary study we propose to identify neuronal networks in rat spinal cord and brainstem that are activated during noxious stimulation with formalin and capsaicin using fMRI. The potential scientific benefit of this project is to obtain better spatial and temporal resolution of neuronal networks involved in pain processing using a non-invasive method which permits multiple measurements to be made in both time and space. Ultimately, characterization of central nervous system networks involved in pain processing will lead to more precise and focused pain treatment.